The electronics field, and particularly the electronic component field, is constantly seeking to improve devices such as capacitors employed in electronic circuits.
There is a particular need for dielectric materials for use in capacitors which exhibit low dissipation factors (or high Q values) at the operating frequencies and have a low temperature coefficient which preferably can be altered depending upon composition to give a negative, positive or zero temperature coefficient (NPO materials). It is preferred that these materials have as high a dielectric constant as possible in a temperature range of from -55.degree. C. to 125.degree. C. However, as Q increases, generally, the dielectric constant decreases such that the attainment of high dielectric constants and high Q has been mutually unattainable. Typical presently available ceramic compositions which have Qs up to about 1,000 at 1 MHz exhibit dielectric constants of only about 20 and temperature coefficients of [.+-.0 to 1000].times.10.sup.-6 /.degree.C.
It is therefore desirable to develop a dielectric material having values of Q of at least 1000 at 1 MHz while attaining dielectric constants of at least 100 at typical operating temperatures.
Of further interest for the commercial manufacture of such dielectric materials, is that the material be sinterable at temperatures of preferably less than 1,000.degree. C. This reduction in sintering temperature not only saves cost in the sintering operation, but also allows less expensive electrodes to be applied to the ceramic material, particularly when employed in a multilayer ceramic capacitor having electrodes between layers which are incorporated prior to sintering.
Dielectric materials based upon strontium titanate and having minor amounts of other oxides such as niobium oxide or tantalum oxide, germanium oxide or zinc oxide and a smaller amount of either bismuth oxide or a mixture of bismuth oxide and other oxides diffused therein are described in U.S. Pat. No. 3,933,668. Also, a dielectric material based upon lead niobate together with oxides of a metal from the group consisting of Bi, Zn, Cd, Pb, Sn, Si, Sb, As, Ge and a combination thereof as well as a metal of the group consisting of Mg, Sr, Ba, Li, Na, K, Rb and Cs is taught in U.S. Pat. No. 3,600,652. Further, Europatent No. 0048871 teaches a ceramic composition consisting of Bi.sub.6 Zn.sub.4 Sb.sub.2 O.sub.18. None of the above compositions exhibit the combined properties being sought.